1. Field of the Invention
The present invention relates to a method for preparing a lithium iron phosphate nanopowder coated with carbon.
2. Description of the Related Art
As technical development and consumption of mobile devices increase, the demand for secondary batteries as energy sources is suddenly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, a long life cycle, and a low self-discharge rate are being commercialized and widely used.
Common lithium secondary batteries use lithium cobalt oxide (LiCoO2) as the main component of a cathode active material. However, since the lithium containing cobalt oxide is unstable and expensive, the mass production of lithium secondary batteries including thereof is difficult.
Recently, lithium iron phosphate (LiFePO4) compound having a voltage of ˜3.5 V and a high volume density of 3.6 g/cm3 when compared to lithium, having a theoretical capacity of 170 mAh/g, as well as having good stability at high temperature, and being cheap when compared to cobalt, is being viewed as a suitable cathode active material for a lithium secondary battery.
However, since a lithium iron phosphate compound has relatively low electron conductivity, when the compound is used as a cathode active material, the internal resistance of a battery may increase. Thus, to increase the conductivity, a conductive material is necessary to be coated thinly on the surface of lithium iron phosphate compound particles.
As methods for preparing the lithium iron phosphate compound, a solid phase method or a liquid phase method such as a hydrothermal synthesis method and a supercritical method is known. Recently, a glycothermal method using a non-aqueous solution such as ethylene glycol or diethylene glycol as a reaction solvent has been developed. To coat a conductive material on the surface of lithium iron phosphate compound particles prepared by the above-described methods, a method of mixing the lithium iron phosphate compound and the conductive material and firing is used. According to this method, the surfaces of the particles are coated with the conductive material during the conducting of a firing process. In this case, the conductive material is not uniformly dispersed on the surfaces of the particles.